This application claims the benefit of the filing date of Finnish Patent Application No. 20010694, filed Apr. 3, 2001.
The invention relates to a bone plate for supporting bone, which is made of a material absorbing partly or entirely into the system and which bone plate comprises an upper surface, lower surface, and at least two fixation holes that extend through the bone plate from the upper surface to the lower surface, through which fixation holes fixation elements can be arranged for fixing the bone plate to bony tissue.
Implants, i.e. bone plates, supporting a healing bone, used in osteosynthesis and made of materials absorbing into the human system are known. They are often bar-like elongated elements in shape. In the following, said elements are referred to as bone plates.
A bone plate is fixed by fixation elements, such as screws, to the bony tissue to be supported, on both sides of a fractured or cracked bone. The bone plate keeps the bone in a correct position so as to allow the bone to heal in the best possible manner. When the bone plate is made of a material absorbing into the system, it need not be removed from the system, thus avoiding surgery to remove the bone plate after the bone has healed. This is naturally advantageous with respect to patient satisfaction, resource load and costs.
The bone plate is thus elongated in shape and comprises at least two, but in most cases a minimum of four, holes extending through the bone plate, to which fixation elements, such as screws, pins or other corresponding fixation elements known per se, are arranged to fix the bone plate and bone to each other. The basic shape of the cross-section of the bone plate is typically a rectangle. In some applications, the cross-section of the bone plate is higher and often also wider at the fixation holes than in the sections between the fixation holes. This design aims at compensating for the decrease in cross-sectional area of the bone plate caused by the fixation holes that would otherwise reduce the tensile strength of the bone plate. U.S. Pat. No. 3,463,148, for instance, discloses a similar solution, in which the cross-sectional area is substantially constant along the entire length of the bone plate. Tensile strength is a significant variable describing the properties of the bone plate, because the bone plate is in a majority of cases arranged on the convex side of the bone. This side is the tension side of the bone, i.e. on this side, tensile load is exerted to the bone and the bone plate fixed to it.
Appropriate fitting of bone sections to each other requires that the bone plate can be shaped exactly according to the shape of the bone sections being fitted together. The lower surface of the bone plate, which is arranged against the bone to be supported, is in most cases concave, i.e. it curves towards the inside, and in the shape of the cylindrical surface of a longitudinal cylinder of the bone plate, whereby it fits the curved shape of the bone. The sections of the bone plate between the fixation holes should also bend and curl to the shape of the bone sections. Fitting is arduous, because the bending and torsional resistance of the sections of the bone plate between the fixation holes are high and shaping requires a great deal of forcexe2x80x94even when using forceps and clamps for fitting. Shaping the bone plate causes a great deal of work during the operation, and consequently, the operation time extends and additional costs accrue. In addition, the fit of the bone plate may remain incomplete, which prevents the use of the bone plate in the application in question, if the bone plate in question is operated to the bone, it may at worst hamper the healing of the bone.
It is an object of the present invention to provide a novel and improved bone plate for use in osteosynthesis and supporting a healing bone.
The bone plate of the invention is characterized in that at least one shaping area reducing the shaping resistance, i.e. bending and/or torsional resistance, of the shape of the bone plate is formed to the section of the bone plate between the fixation holes, the thickness of the edge section of which shaping area is substantially smaller than that of its mid-section.
The essential idea of the invention is that in the section of the bone plate between the fixation holes, there are one or more sections reducing the shaping resistance of the bone plate (later shaping area). Further, the essential idea of the invention is that the thickness of the edge section of the cross-section of the shaping area is smaller than the thickness of the section at the centerline of the bone plate. Further, the essential idea of a preferred embodiment of the invention is that the length of the shaping area is substantially equal to the length of the bone plate section between the fixation holes. Further, the essential idea of a second preferred embodiment of the invention is that the maximum width of the shaping area is greater than the basic width of the bone plate.
The invention provides the advantage that the shaping resistance, i.e. bending and/or torsional resistance, of the bone plate is made low, whereby the shaping of the bone plate is essentially easier than in the prior art, without essentially reducing the tensile strength, however. When the shaping area is the longest possible, i.e. essentially as long as the bone plate section between the fixation holes, shaping the bone plate is even easier. By widening the edge sections of the shaping area to make their maximum width greater than the basic width of the bone plate, it is possible to increase the tensile strength of the shaping area without essentially compromising the good shaping properties.